Positive relationship between passive muscle stiffness and rapid force production

Area of Science:

• Biomechanics
• Muscle Physiology
• Sports Science

Background:

• Understanding the relationship between passive muscle properties and dynamic performance is crucial for optimizing athletic training and injury prevention.
• Previous research has explored muscle size and strength, but the role of passive muscle stiffness in explosive force generation remains less clear.

Purpose of the Study:

• To investigate the association between resting muscle shear modulus, maximal joint torque, and the rate of torque development (RTD) in the medial gastrocnemius (MG) muscle.
• To determine if passive muscle stiffness influences maximal voluntary contraction (MVC) torque or the speed of force production.

Main Methods:

• Twenty-seven healthy adults underwent magnetic resonance imaging (MRI) for muscle cross-sectional area (CSA) and ultrasound shear wave elastography for MG shear modulus measurement.
• Participants performed maximal isometric plantar flexion tests to assess MVC torque and calculate normalized RTD over various time intervals (0-200 ms).

Main Results:

• MG muscle cross-sectional area showed a significant correlation with maximal voluntary contraction torque (r=0.572).
• MG shear modulus was not significantly correlated with maximal voluntary contraction torque.
• A significant positive correlation was found between MG shear modulus and normalized rate of torque development across all measured time intervals (r=0.460-0.496).

Conclusions:

• Passive muscle stiffness, as indicated by shear modulus, is not directly related to maximal muscle force output.
• Higher passive muscle stiffness in the medial gastrocnemius may contribute to faster rates of torque development, suggesting a role in explosive movements.